1. Field of the Invention
The present invention relates to an apparatus for and a method of controlling an output of a laser diode in an optical recording/reproducing apparatus, and more particularly, to an apparatus for and a method of controlling an output of a laser diode in accordance with a sampled signal of the output having a predetermined frequency.
2. Description of the Related Art
Various types of recording media having a great amount of data recording capacity have been developed for use in optical recording apparatuses, such as CD-R, CD-RW, Magnetic Optical Disc Drive (MODD), DVD-Digital Versatile Disc Random Access Memory (DVD-RAM), DVD−RW and DVD+RW. These optical recording apparatuses use a laser diode for reading data from and writing data onto the recording medium, and the performance of each optical recording apparatus depends on how well an output of the laser diode is controlled. In order to control the output of the laser diode at an optimum level, the shape of a write pulse must be accurately controlled because the shape of the write pulse is different depending on each type of the optical recording apparatus.
FIG. 1 is a block diagram of a general laser diode output control apparatus. Referring now to FIG. 1, a reference numeral 120 indicates a write waveform generator for generating a write pulse so as to form a space or mark corresponding to recording data on a disc 180. A reference numeral 140 denotes a laser diode driving unit for controlling an output of a laser diode 160 according to the write pulse generated in the write waveform generator 120. Here, the recording data input to the write waveform generator 120 is a non return-to-zero inverted (NRZI) signal, and the write pulse output from the laser diode driving unit 140 is a combination of a first pulse, a last pulse, a cooling pulse, and a multi-train pulse in the case of DVD-RAM.
An auto laser power controller (APC) 200 includes a photo diode (PD) 202, a variable gain amplifier (VGA) 204, a comparator 206, an up/down counter 208 and a digital-to-analog converter (DAC) 210.
The PD 202 receives light reflected from the disc 180 and generates an electrical signal corresponding to the gain of the received light. The VGA 204 amplifies the electrical signal with a predetermined gain and converts the amplified electrical signal into a voltage signal. The comparator 206 compares the voltage signal of the VGA 204 and a reference power value Vref and outputs a determination signal in response to the comparison between the voltage signal and the reference value Vref.
The up/down counter 208 counts up/down according to the determination signal output from the comparator 208. In detail, the up/down counter 208 counts down when the determination signal output from the comparator 206 is at a low level representing that the voltage signal of the VGA 204 is greater than the reference power value Vref. In contrast, the up/down counter 208 counts up when the determination signal is at a high level representing that the voltage signal of the VGA 204 is smaller than the reference power value Vref. The counted output signal of the up/down counter 208 is applied to the laser diode driving unit 140 via the DAC 210. The laser diode driving unit 140 controls an output level of the laser diode 160 according to the counted output signal applied to the DAC 210.
The APC circuit 200 shown in FIG. 1 detects a difference between the reference power value Vref and the present power value of the laser diode 160 detected by the PD 202 and controls an output level of the laser diode 160 according to the difference.
Since the conventional laser diode output control apparatus shown in FIG. 1 uses the up/down counter 208 for counting the voltage signal after the reference power value Vref is compared with the present power value, it is disadvantageous that the processing speed of the voltage signal cannot be increased with the up/down counter 208 and peripheral components as the reproducing and recording speed of the optical medium and the optical recording and reproducing apparatus increases. Moreover, the speed and the range of controlling the optical output of the laser diode are limited by a working speed of the up/down counter 208 since the up/down counter 208 processes the voltage signal at a constant speed regardless of the type of the optical medium and the reproducing and recording apparatus. Further, if the recording speed of the medium increases, the width of a write pulse is reduced. However, the up/down counter 208 cannot generate a counted signal for the reduced write pulse.